The invention refers to a method for coding a sequence of digitized images as well as to a method for decoding such a sequence. Furthermore, the invention refers to a coding apparatus and a decoding apparatus as well as to a system including a coding apparatus and a decoding apparatus.
For digital video coding with high coding efficiency, so-called motion compensation is used. In motion compensation, motion vectors between similar image blocks in the image to be coded and a corresponding reference image are determined. A motion vector references a reference block in the reference image having the same or very similar image information as a block in the image to be coded. Motion compensation takes into account that many structures in an image are only shifted and do not change from one image to the next. Based on an image block and its corresponding reference block, the prediction error between those blocks is calculated and used for coding.
Under certain circumstances, there is a need to restrict the reference blocks which are used for prediction to certain areas in the reference image. E.g., a video coding process is described where a gradual intra refresh of only a region in each image is performed, as described in the following documents:
Kimihiko Kazui, Junpei Koyama, Akira Nakagawa, “Evaluation result of JCTVC-B031”, ISO/IEC JTC1/SC29/WG11 and ITU-T SG16 WP3, document JCTVC-C021/M18028, Guanzhou, China, October 2010.
Kimihiko Kazui, Junpei Koyama, Akira Nakagawa, “Draft description of proposed syntax and semantics for very low delay coding”, ISO/IEC JTC1/SC29/WG11 and ITU-T SG16 WP3, document JCTVC-D053/M18800, Daegu, Korea, January 2011.
Kimihiko Kazui, Junpei Koyama, Akira Nakagawa, “Benefit of the new syntax and semantics for very low delay coding in HEVC”, ISO/IEC JTC1/SC29/WG11 and ITU-T SG16 WP3, document JCTVC-D054/M18801, Daegu, Korea, January 2011.
As a consequence, an image comprises an updated area with already intra-coded regions and a non-updated area with regions not yet intra-coded. In this scenario, it is prohibited to predict image blocks in the updated area of the image from reference blocks in the non-updated area of the reference image. Otherwise, in case of random access into the video stream, these references would result in mismatches since the blocks in the non-updated area are not correctly decoded.
In German Patent Application No. 10 2007 049 351 A1, a method for generating a coded video stream based on several input video streams is disclosed. It is mentioned in this document that the prediction for coding the pictures in one video stream shall only be performed within the boundary of those pictures.